There is a concern by some who use chlorine in chemical production facilities that there is an occupational hazard of inhaled chlorine. The purpose of this project is to determine the distribution of inhaled CL2 in healthy men and women during oral and nasal breathingat respiratory flows characteristic of rest and exercise. The specific aims are: Develop a bolus inhalation method to safely and indirectly measure Cl2 distribution in the respiratory tract. This method will be tested on 3-5 subjects who are breathing quietly through their nose. Determine the effect of different inhalation concentrations from 0.3 to 3.0 parts per million on the Cl2 distribution in a group of five subjects who are breathing quietly through their nose. Determine the change in Cl2 distribution during oral breathing when respiratory flow increases from a resting level to a level characteristic of light exercise in a group of ten subjects who are breathing through their nose. (The subjects will not be exercising) Determine whether a change from nasal to oral breathing increases the fraction of inhaled Cl2 that reaches the lower airways in a group of ten subjects who are breathing quietly.